Hyperfine structure of the $\mathbf{A^{1}\Pi}$ state of AlCl and its relevance to laser cooling and trapping

Abstract

The majority of molecules proposed for laser cooling and trapping experiments have $\Sigma$-type ground states. Specifically, $^2\Sigma$ states have cycling transitions analogous to D1-lines in alkali-metal atoms while $^1\Sigma$ states offer both strong and weak cycling transitions analogous to those in alkaline-earth atoms. Despite this proposed variety, to date, only molecules with $^2\Sigma$-type ground states have successfully been confined and cooled in magneto-optical traps. While none of the proposed $^1\Sigma$-type molecules have been successfully laser cooled and trapped, they are expected to have various advantages in terms of exhibiting a lower chemical reactivity and an internal structure that benefits the cooling schemes. Here, we present the prospects and strategies for optical cycling in AlCl -- a $^1\Sigma$ molecule -- and report on the characterization of the $A^{1}\Pi$ state hyperfine structure. Based on these results, we carry out detailed simulations on the expected capture velocity of a magneto-optical trap for AlCl. Finally, using {\it ab initio} calculations, we identify the photodissociation via a $3^1\Pi$ state and photoionization process via the $3^1\Sigma^+$ state as possible loss mechanisms for a magneto-optical trap of AlCl.